Java 写时拷贝容器CopyOnWriteArrayList的测试---Jerry Wang

测试代码：

package copyOnWriteArrayListTest; import java.util.ArrayList; import java.util.List; import java.util.concurrent.CopyOnWriteArrayList; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; class AddThread implements Runnable { private List<Double> list; public AddThread(List<Double> list) { this.list = list; } @Override public void run(){ for ( int i = 0; i < 10000; i++){ list.add(Math.random()); } } } public class CopyOnWriteArrayListTest { public static final int THREAD_POOL_SIZE = 2; public static void main(String[] args) throws InterruptedException { // List<Double> list = new ArrayList<>(); List<Double> list = new CopyOnWriteArrayList<>(); ExecutorService es = Executors.newFixedThreadPool(THREAD_POOL_SIZE); es.execute(new AddThread(list)); es.execute(new AddThread(list)); es.shutdown(); Thread.sleep(4000); System.out.println("OK, list length: " + list.size()); } }

输出结果：

OK, list length: 20000

如果把支持写时拷贝的list替换成普通的ArrayList：

List list = new ArrayList<>();

因为两个线程同时对这个普通的ArrayList进行写操作，结果如下：

OK, list length: 17578

看下CopyOnWriteArrayList实现源代码里Add方法的实现：

/** * Appends the specified element to the end of this list. * * @param e element to be appended to this list * @return {@code true} (as specified by {@link Collection#add}) */ public boolean add(E e) { synchronized (lock) { Object[] es = getArray(); int len = es.length; es = Arrays.copyOf(es, len + 1); es[len] = e; setArray(es); return true; } }

lock初始化的地方：

final transient Object lock = new Object();

---来自腾讯云社区的---Jerry Wang